No official cause of death has been given, but if it turns out a vein failure was to blame, that could mute the impact of the bungle on the growing debate over lethal-injection drugs nationwide.

After Lockett's death, a spokesman for the Texas Department of Criminal Justice said the agency has no plans to change its protocol.

"The Oklahoma incident does not appear to be related to the choice of drugs," he noted.

Levin said that regardless of why Lockett's lethal injection went wrong, executions in Oklahoma and Texas have something in common: Both states refuse to say where they obtain their execution drugs.

She also noted that while Texas has been using pentobarbital to kill prisoners, it has a stockpile of midazolam, the sedative used on Lockett and in the controversial execution of Dennis McGuire in Ohio earlier this year.